See the contribution of various ionization states to pKa and visualize all ionized microspecies as a function of pH

"The best software for routine logD and pKa predictions!"Susan Winks (H3D)

"We chose [Percepta] because it is the industry standard for pKa and logD prediction…it will help us filter out compounds with undesirable physicochemical properties. The batch processing option will allow us to quickly triage large compound sets."Dr. Tom Carter (University of Oxford)

GALAS Algorithm

A database of ionization centres, interaction constants, and interaction calculation methods are used to simulate a complete distribution plot of produce a full range of protonation states of the molecule at different pH conditions. pH dependency of net molecular charge, distribution of protonation states, and the average charge of each ionization centre is provided.

Acid Dissociation Constant (pKa) Calculator Features

Calculate the acid dissociation constant (pKa) under standard conditions (25°C, zero ionic strength) in aqueous solution for all stages of ionization from structure, SMILES string, or chemical name

See the ionization reaction and pKa microstants for all ionizable species

Calculation protocol provides information about structural fragments used for the calculation of pKa

Visualize a plot of protonation states vs pH

ACD/pKa automatically checks for tautomeric forms

A Machine Learning pKa Calculator

Experimentally determined pKa values can be used to train the algorithms using the machine learning capabilities of the software. This both improves prediction accuracy and makes the model more relevant to your chemical space or project.

Both the Classic and GALAS algorithms offer machine learning (training) and you don't have to be a computational chemist to use them.

Do you have a large curated set of experimentally measured pKa values?
Our development team is happy to collaborate with you to expand the applicability domain of our algorithms.

Deployment Options

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Desktop/Thick client

Software installations for individual computers with a graphical user interface. Full physicochemical, ADME and toxicity calculator modules are available (with training capabilities) including the PhysChem Profiler bundle.

Batch

Screen tens of thousands of compounds with minimal user intervention—compatible with Microsoft Windows and Linux operating systems (OS). Plug-in to corporate intranets or workflow tools such as Pipeline Pilot.

Software from ACD/Labs was used in the prediction of physical and chemical properties, and retention modelling and optimization.Read more

What is the acid dissociation constant Ka?

The acid dissociation constant (Ka, also known as the acid-ionization constant) is a quantitative measure of the strength of an acid in solution (i.e. a measure of the tendency of a molecule to release H­+ and generate a hydronium ion (H3O+). A strong acid will completely dissociate in water (equilibrium favors the right hand of the equation below), while weak acids will not.

HA + H2O &rlhar; H3O+ + A-

Ka is the equilibrium constant that describes the dissociation of a molecule and is expressed as a ratio of concentrations of the various species present

What is pKa?

The acid ionization constant (Ka) varies by orders of magnitude. It is therefore more intuitive to refer to such extreme numbers on a logarithmic scale. By convention the p in pKa was introduced to denote the negative logarithm (base 10).

pKa = -log10 Ka

Ka values are converted to pKa values as follows:

Phenol:pKa = -log (1. 8 × 10-10) = 10.0

Acetic acid:pKa = -log (1.8 × 10-5) = 4.8

There is no intrinsic reason to rule out pKa values less than 0 or greater than 14. For example, sulfuric acid, H2SO4, has a negative pKa for the loss of its first proton:

H2SO4 → HSO4- + H+ (pKa < 0)

Experimental determination of pKa values, however, is usually limited to between 1 and 13.

How are pKa and pH related?

pKa (the acid dissociation constant) describes the inherent property of a compound or ionizable functional group to lose H+ and generate hydronium ions (H3O+).

How are pKa values used?

Synthetic chemists use the acid dissociation constant to understand what substances can be used to protonate or deprotonate a compound, to assist a reaction. In biochemistry pKa helps scientists understand the activity of enzymes and the stability of proteins.

In pharmacology, ionization of a compound changes its physical behavior and affects macro properties such as aqueous solubility and lipophilicity. pKa values are also used to understand more complex ADME characteristics.

pKa is used by chromatographers to select the appropriate pH of the mobile phase (buffer) for separations.

In environmental sciences acid-base equilibria of humic acids help establish the potability and treatment of water and provide information about the health of waterways such as lakes and rivers.

Ready to learn more?

Contact us to request a demonstration of our software, or to answer any questions you may have.